[OSM-talk] How to georeference OSM Mapnik tiles?

[Rahkonen Jukka]

Hi,
 
I would like to convert some OSM tiles to geotiff format, but I wonder
how can I get the georeferencing information I need for it. What I would
need to know is:
- Which projection the tiles are in (EPSG code or projection parameters)
- Pixel size for each zoom level
- What is the anchor point of the tile and its corresponding coordinates
 
How can I find out those data for, let's say this image tile:
 
http://b.tah.openstreetmap.org/Tiles/tile.php/15/18653/9484.png
 
Number 15 is obviously the zoom level, and from values 18653 and 9484 I
guess I should be able to conclude somehow the anchor point.  But in
what projection the tiles are, and what are the units and pixel sizes
used for each zoom level?  Or do I have some better or more direct way
for getting an excerpt of Mapnik layer in geotiff format?
 
-Jukka Rahkonen-
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